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Thread: Any GPS afficionados out there?

  1. #1
    Flashaholic* kaichu dento's Avatar
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    Default Any GPS afficionados out there?

    I just picked up a Garmin Nuvi 205 at a yard sale and was hoping I'd be able to get maps for Alaska/Canada and Japan. I was surprised that although it is unusable for navigation purposes, there are a lot of fairly small towns in Japan shown.

    Any help appreciated and I'm curious how many people use GPS in their car on a daily basis.
    Marduke - Solitaire...I've seen matches which are brighter AND have a longer runtime. 光陰矢の如し

  2. #2

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    Quote Originally Posted by kaichu dento View Post
    I just picked up a Garmin Nuvi 205 at a yard sale and was hoping I'd be able to get maps for Alaska/Canada and Japan. I was surprised that although it is unusable for navigation purposes, there are a lot of fairly small towns in Japan shown.

    Any help appreciated and I'm curious how many people use GPS in their car on a daily basis.
    I would check Garmin's website for maps.

    Even better, IMO, is the combination of iPhone 4 and the Navigon app. My phone is always with me, the app integrates with my contact list and Google search, has live traffic data, and you get free lifetime map updates.

    I really like having the maps in the app (as opposed to Google maps) because it works even in places like Death Valley where there's no cell coverage. If you can see the sky, you've got GPS coverage.

  3. #3

    Default Re: Any GPS afficionados out there?

    Before the economy tanked I used survey spec GPS. Like sub-millimeter horizontal control and 4mm vertical. Used static setups (15 mins to an hour over a spot) and RTK (Real Time Kinematic) for boundary surveys.

    Few things most don't know about GPS:
    There are actually 2 constellations up there. Ours and the Russian system called Glonass. Some of the high end survey packages will lock onto both sets and cross-check data for faster lock downs.

    Positional accuracy is iffy at best, one must have a baseline location to correct (or translate) the data into solid locational data. Relative positional accuracy is mind-blowingly accurate, I've seen mile long baselines with 1 to 100000000 (billionths) precision.

    Vector data (movement) again is spotty in terms of overlay unless tied to a known point. Relative vector data (speed, heading) are supremely accurate. Fire up a GPS receiver in your car, get 4-5 sats with good signal and you can take the speed reading to the bank, it's right simply because math does not lie. We never did the math to see if elevation changes effected the land speed readout, tho you'd have to be going down or up a REALLY steep hill to see a significant difference.

    Minimum theoretical satellites for horizontal fix is 2, IF your receiver allows you narrow down your location(two possible points). Three satellites will give you a rough vertical. It's always the more the merrier with GPS. I locked down 20+ sats with a LOCUS system one day while near the top of a small mountain, my rover was capable of one location every 1/10th of a second with sub-millimeter accuracy. Keep in mind this (at the time) was a 100k$ setup and had GLONASS compatability.

    Backscatter (reflected signals) can confuse the receiver, eyeball your selected receiver location for any possible sources of backscatter. Also, high tension powerlines are fountains of bizarre radiation and WILL monkey with GPS.

    Hope that didn't bore people to tears.
    I seem to have misplaced my occipital lobe, and as such cannot search for it. Do you see my dilemma?

  4. #4
    Flashaholic* mvyrmnd's Avatar
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    Default Re: Any GPS afficionados out there?

    Quote Originally Posted by brembo View Post
    Hope that didn't bore people to tears.
    Hardly. It's the most interesting thing I've read since this morning!

  5. #5

    Default Re: Any GPS afficionados out there?

    If the Nuvi 205 you picked up was originally sold in the US, then it should have the Canadian maps already. The map pack would be the city navigator north america NT. For Japan, you will need to find 3rd party maps.


    [Remainder of post removed. Discussion of pirated (stolen) items is not permitted - please read Rule 11. - DM51]
    Last edited by DM51; 07-21-2011 at 07:30 AM.

  6. #6

    Default Re: Any GPS afficionados out there?

    Quote Originally Posted by brembo View Post
    Before the economy tanked I used survey spec GPS. Like sub-millimeter horizontal control and 4mm vertical. Used static setups (15 mins to an hour over a spot) and RTK (Real Time Kinematic) for boundary surveys.

    Few things most don't know about GPS:
    There are actually 2 constellations up there. Ours and the Russian system called Glonass. Some of the high end survey packages will lock onto both sets and cross-check data for faster lock downs.

    Positional accuracy is iffy at best, one must have a baseline location to correct (or translate) the data into solid locational data. Relative positional accuracy is mind-blowingly accurate, I've seen mile long baselines with 1 to 100000000 (billionths) precision.

    Vector data (movement) again is spotty in terms of overlay unless tied to a known point. Relative vector data (speed, heading) are supremely accurate. Fire up a GPS receiver in your car, get 4-5 sats with good signal and you can take the speed reading to the bank, it's right simply because math does not lie. We never did the math to see if elevation changes effected the land speed readout, tho you'd have to be going down or up a REALLY steep hill to see a significant difference.

    Minimum theoretical satellites for horizontal fix is 2, IF your receiver allows you narrow down your location(two possible points). Three satellites will give you a rough vertical. It's always the more the merrier with GPS. I locked down 20+ sats with a LOCUS system one day while near the top of a small mountain, my rover was capable of one location every 1/10th of a second with sub-millimeter accuracy. Keep in mind this (at the time) was a 100k$ setup and had GLONASS compatability.

    Backscatter (reflected signals) can confuse the receiver, eyeball your selected receiver location for any possible sources of backscatter. Also, high tension powerlines are fountains of bizarre radiation and WILL monkey with GPS.

    Hope that didn't bore people to tears.
    thanks brembo.
    can you get backscatter off aluminium in a boat?

    i learned a bit about gps back when they had selective availability. i understood speed to be calculated using the doplar effect, and so even when they only gave us ' 40 metre position accuracy 95 percent of the time' speed was always spot on.

    so a surveyer, with a 100k dollar unit, can position to a millimetre ? that is just so cool.
    i spose first they use gps to work out the location of the satellites relative to known terrestial locations then work out your location relative to the satellites.

    cheers
    Last edited by beerwax; 07-21-2011 at 04:45 PM.

  7. #7

    Default Re: Any GPS afficionados out there?

    Quote Originally Posted by beerwax View Post
    thanks brembo.
    can you get backscatter off aluminium in a boat?

    i learned a bit about gps back when they had selective availability. i understood speed to be calculated using the doplar effect, and so even when they only gave us 40 metre position accuracy 95 percent of the time speed was always spot on.

    so a surveyer, with a 100k dollar unit, can position to a millimetre ? that is just so cool.
    i spose first they use gps to work out the location of the satellites relative to known terrestial locations then work out your location relative to the satellites.

    cheers
    I dunno about the doppler effect being used in GPS for speed calcs. My strong area was always in time-stamp vector driven calculations. Doppler is used but well beyond my knowledge base.

    An AL boat will send signal all over the place. Put the antenna facing upwards on something that blocks any possibility of signal being relected upwards to it (like on top of a cooler or something). Most units have a screen with two circles on it, outer ring is the horizon and the inner ring is a 45 degree zenith. If there are a lot of sats bunched in the 45 ring, expect weird data at times. With a handheld or general navigation GPS backscatter will simply slow it's lock down and give slightly off numbers, on the order of a few feet. With precision measurements that surveyors have to attach a signature and liability too, a wonky satellite signal is a no-no. Often times I'd have to go into the data files and remove a satellite that was hovering near the horizon due to spotty reception.


    The old SAS stuff really didn't effect surveyors all that much. The really tight locations were all post-processing. Back in the day of 486 processors a 1/2 day data collection could tie up a high-end station for hours translating and rotating the data. In 2010 it took longer to get the data out of the units via firewire than it took the computer to r and t. All we cared about was relative location and we would set "control" to base our traverse and "sideshots" (angular observations from a control point). A "control station" would be placed on a control point and allowed to collect data all the time a rover was in use. The rover is in communication all the time with the control station and the time of any data point collection is synched. So even if a Titan were to reach down and rip the entire site and toss it two miles it would not matter a lick to a surveyor. The relative accuracy would be intact.

    A few surveys we did had to be tied down to known and "real" coordinates. We used Geodetic Survey markers and translated to that system once back in the office (or truck if engineers needed onsite data).

    I only ever staked out one house with GPS, it was an architect that was so incredibly anal about solar orientation that I ended up having to research the suns traverse. I could have doe it with a traditional total station but this guy wanted GPS because "it is better". I personally don't argue with lasers but whatever the lease on the RTK stuff cost him a bundle.

    If any of this stuff interests you have a look at Cyrax systems. Scanning technology with 2mm accuracy. It's amazing stuff. I demoed one for a basement retrofit(structural) and was blown away with the amount of data these things parse. A good engineer can do anything with a proper Cyrax scan. The newest of the new total stations have this ability built-in, millimeter GPS built-in AND calibrated digital cameras that will overlay the photos as a "skin". Star Treks "tricorder" technology is quickly approaching.
    I seem to have misplaced my occipital lobe, and as such cannot search for it. Do you see my dilemma?

  8. #8
    Flashaholic* kaichu dento's Avatar
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    Default Re: Any GPS afficionados out there?

    Some very interesting info from Brembo and I hope others will come up with the nugget of knowledge that allows me to find the maps somewhere online.
    Marduke - Solitaire...I've seen matches which are brighter AND have a longer runtime. 光陰矢の如し

  9. #9
    *Flashaholic* gadget_lover's Avatar
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    Default Re: Any GPS afficionados out there?

    It is my understanding that most maps are based on data obtained from governments or governmental bodies. Some map data is given to the GPS people for free, while some governments make it very difficult/expensive to use their mapping data.

    Since garmin does not have map info for Japan, I suspect it falls into the later category.

    There are programs for your PC that will allow you to scan in a physical map and translate it to map points that the Garmin can use. It would be cheaper and easier to locate a GPS that is already set up for use in Japan.

    Dan
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  10. #10
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    Default Re: Any GPS afficionados out there?

    Check out OSM (OpenStreetMap). They have various maps (all of which are free) available for download which works with Garmin GPS receivers.

    http://wiki.openstreetmap.org/wiki/O...armin/Download

    If you're willing to shell out cash, Garmin sells them.
    Last edited by mina; 10-06-2011 at 11:12 PM.

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